Bituminous paving apparatus



Mayz, 9 D. R. DAVIN 3,316,821

BITUMINOUS PAVING APPARATUS Filed May 15, 1964 Donald R. Devil? UnitedStates Patent O 3,316,821 BITUMINOUS PAVING APPARATUS Donald R. Davin,Shelbyville, Ill., assignor to Blaw-Knox Company, Pittsburgh, Pa, acorporation of Delaware Filed May 13, 1964, Ser. No. 367,102 1 Claim.(Cl. 94-46) This invention relates to bituminous pavers and particularlyto screeds and associated equipment for paving with bituminous concrete.The invention is particularly adapted for use in connection with pa ershaving a tractor behind which the screed is towed, the screed restingupon and riding over freshly placed bituminous material.

A common form of bituminous paver employs a selfpropelled tractor havinga hopper to receive the bituminous mix and various Spreaders, conveyorsand the like to deposit the bituminous mix behind the tractor and acrossthe width of the section which is to be paved. Such tractors customarilyinclude a screed assembly which is towed or carried at the rear of thetractor. Ordinarily, the screed is freely floating. It is pulled byforwardly extending arms which permit the screed to seek a level whereit is in equilibrium between the various forces acting upon it, such asits own weight, the upward force of the underlying bituminous material,and the forces applied by the pull arms. A pile of bituminous materialis loosely deposited ahead of the screed by the tractor. As the screedadvances, it strikes off excess material and carries it forwardly. Thescreed rides over and the bituminous material not struck off iscompacted by the screed into a mat which is ordinarily compacted furtherby rolling. One form of screed is provided with a sole plate which is inthe nature of a large fiatiron. A tamper is provided extending acrossthe width of the screed along the forward edge of the sole plate tocompact the bituminous mix and tuck it beneath the sole plate forsmoothing.

Such tampers have customarily been vertically positioned and have had ashield in front of them extending forwardly and upwardly to prevent thebituminous material from crawling upwardly upon the tamper and cloggingthe mechanism.

I have invented new and useful improvements in bituminous paving screedaparatus in which I provide a screed, a sole plate, reciprocating tampermeans positioned at an angle to the vertical so that the lower end ofthe tamper is ahead of its upper end and a curved shield memberpositioned forwardly of the tamper means. I prefer to mount a tamper atan angle to the vertical for axial reciprocating movement downwardly andforwardly and then upwardly and backwardly. I preferably dispose thetamper with its upwardly end slanted to the rear at an angle of abouttwenty degrees from the vertical. I preferably mount the tamper with itslower portion in juxtaposition with the forward edge of the sole platewhereby entrance of bituminous material between the sole plate and thetamper is prevented. I prefer to dispose the tamper shield meansforwardly of the tamper with the bottom of the tamper and the bottom ofthe tamper shield in juxtaposition whereby entrance of bituminousmaterial between the tamper and the tamper shield is prevented. I formthe shield without any substantial uncurved sections and preferablycurve the shield forwardly from a mid-point to the top and bottom edges.The shield thereby extends from its bottom edge upwardly and 'rearwardlyto a midpoint whence it extends upwardly and forwardly. I furtherpreferably provide agitator means forwardly of the tamper shield meansin position to receive bituminous material which circulates forwardlyfrom the tamper shield means. I prefer to provide screw means disposedforwardly of the screed means in position to receive bituminous materialwhich is pushed upwardly on the shield and forwardly therefrom wherebythe bituminous material is remixed and redistributed by the screw means.I further prefer to provide a bevel of chamfer on the lower edge of thetamper whereby the bottom surface of the tamper is of relatively narrowwidth. I further prefer to dispose the beveled surface so that the upperedge of the beveled surface is forwardly of the bottom edge of thebeveled surface. I also prefer to provide screed extension means havingthe same configuration as the central portion of the screed whereby thescreed may conveniently be extended by fixing additional sectionsthereto.

Other details, objects and advantagesof my invention will become moreapparent as the following description of a present preferred embodimentthereof proceeds.

In the accompanying drawings I have illustrated a present preferredembodiment of my invention in which FIGURE 1 is a side view of abituminous paver embodying my invention;

FIGURE 2 is a view of a portion of the screed shown in FIGURE 1 lookingforwardly from behind the paver; and

FIGURE 3 is an end view of the screed structure shown in FIGURE 1,illustrated in greater detail.

The paver comprises a. tractor 1 propelled by an engine 2, throughappropriate power transmissions. An operator seat 3, a steering wheel 4,and other controls are placed rearwardly of the engine in position forthe operator to observe the paving action while operating the payer.Tractor 1 is supported by a rear wheel 5 upon each side of the tractorand front wheel 6 on each side of the tractor. Each rear wheel includesa pneumatic tire mounted upon a steel rim fixed to a driven axle. Fromwheels 6 have solid or semi-pneumatic tires and are connected tosteering wheel 4 through a linkage so that they can be turned. to oneside or the other by the operator, thereby steering the tractor. Amaterial receiving hopper 7 is provided at the forward end of thetractor and has sides 8 formed of steel plates. Hopper 7 is filled fromtrucks which deliver bituminous paving mix to the job site from a batchplant and dump it into hopper 7. Conveyors are provided within thetractor body and act to move bituminous mix from hopper 7 rearwardly anddeposit the mix just ahead of a screw conveyor 9 which extendstransversely across the rear of the tractor in front of the screedstructure. Screw conveyor 9 is mounted on brackets 10 which are fastenedto the tractor frame. Conveyor 9 is driven by engine 2 through clutchesand has one half reverse threaded on the other half so that rotation ofconveyor 9 urges material from the center of the paver toward the twosides of the paver. Each half is under separate control of the operatorso that either or both halves of conveyor 9 may be operated at any giventime. p

A screed pull arm 11 is fitted on each side of the tractor. A stud 12extends from each pull arm 11 and is in front of a vertical beam 13mounted on each side of the tractor at a forward point near the hopper.A roller bearing 14 is fitted upon stud 12 so that the arm mayconveniently be moved up and down despite forces developed by a rearwardpull upon arm 11. a

A stud extends outwardly from pull arm it behind vertical beam 13. Studs12 and 15 thereby resist substantial forward and back movement by pullarm 11. A clevis 16 is pivoted to pull arm 11 at its forward end and isconnected to a piston rod 17 of hydraulic cylinder '18. Cylinder 18 isin turn connected by a rod 19 to the frame of tractor 1. Hydraulic fluidis supplied under pressure to the top and bottom of each cylinder 18, toenable the forward end of each pull arm to be moved up and down. Eachpull arm 11 extends rearwardly of the tractor and terminates in adownward extension 24). Each end of the screed is pivoted at a pivotpoint 21 to the downward extension of one of the pull arms. The screedcomprises a box-like screed body 22 having a sole plate 23 mounted toits lower face. An upwardly extending bracket 24 is welded to the screedbody at each end and is pivoted to the pull arm at pivot point 21. Aplatform 25 extends rearwardly from the screed body on each sideto'enable a workman to stand upon it and ride with the paver.

Each bracket 24 terminates in fitting 26 having a bushing 27 at itsupper end. A shaft 28 is rotatably mounted in bushing 27 and is rotatedby a crank 29, connected to one end of shaft 28; A toothed wheel 30 isalso fitted to shaft 28 and crank 29 and has teeth 31 and slots 32around its circumference. A detent 33 is pivotally mova ble up and downand may be dropped into one of slots 32 to lock shaft 28 in any givenposition. Shaft 28 is connected through a universal joint 34 to one endof a turnbuckle assembly 35. The other end of the turnbuckle 36 isconnected to the inner face of pull arm 11.

A longitudinal tamper 37 is mounted upon the forward side of the screedfor reciprocating movement. Tamper 37 is positioned at a slope to thevertical with its lower end forward of its upper end. The tamper ispreferably positioned at an angle of about 20 from the vertical. It ismounted for reciprocating up and down movement along its axis. Since itis at a slope, it moves alternately downwardly and forwardly and thenupwardly and rearwardly. A tamper drive shaft 38 is rotatably mounted ina pillow block 39 and cap 40 fitted at the top of the'screed. Shaft 38carries eccentrics upon which a crank connected to the upper end oftamper 37 is journaled. Such details of construction are well known andfor purposes of simplicity are not illustrated or described herein.

The lower end of tamper 37 has a chamfer 41 so that the bottom surfaceof the tamper is relatively thin. The angle of chamfer 41 is at asomewhat larger angle to the tamper than the angle of the tamper to thevertical. The upper edge of chamfer 41 is thereby forward of the loweredge of chamfer 41.

r A tamper shield 43 is positioned forwardly of the tamper and fastenedto the screed by brackets 44. Shield 43 has a lower section 45 which isadjacent to the lower portion of tamper 37. From its lowermost edge thetamper shield extends upwardly and rearwardly until it reaches amid-point 46 of the tamper shield whence the tamper shield extendsupwardly and forwardly.

A heater 49 is provided to preheat the screed box before the screed isplaced into service. A fan 5%) delivers air to the heater and thenforces the heated air into and through the screed and sole plate. Ahandrail 51 is mounted on the screed, and a turnbuckle linkage 52 isinstalled to maintain longitudinal stiffness of the screed.

Screed extensions 53, 54 and 55 are provided to lengthen the screedthereby increasing the width being paved. The extensions areconveniently comprised of sole plates 23', 23", 23" and box sections22', 22", and 22", respectively. Corresponding extensions are fitted toscrew conveyor 9 to extend it concurrently with the screed. A liftingcable 56 extends over a sheave 57. One end of cable 56 is attached topull arm 11 and the other end to a winch controlled by the operator.

When the paver is in operation, bituminous mix is delivered to hopper 7,and the tractor moves forward. While it is advancing, bituminous mix isdelivered in front of screw conveyor 9 by the internal conveyors. Screwconveyor 9 is operated to keep an adequate quantity of the mixdistributed across the front of the screed. The conveyors are operatedto keep an excess quantity of bituminous mix piled up in front of thescreed. As the paver advances, the screed strikes off the excessbituminous material. The material which is not struck off is tamped downby tamper 37 as it passes over the bituminous material and reciprocatesbetween the tamper shield and wear plate 43 at the forward edge of soleplate 23. The tamped material is further compacted and smoothed by thesliding motion of sole plate 23 as it passes over the material. Theexcess material which is struck off is necessarily carried forwardly infront of the screed. As the screed advances, the excess material infront of tamper shield 43 is forced upwardly by the slope of the tampershield until the material reaches the midpoint do of the shield.Thereafter the excess is forced upwardly by the pressure of excess mixfrom below, but by reason of the shape of the tamper shield, the mix isforced upwardly and forwardly from mid-point 46 until it falls from theupper portion 47 of the tamper shield onto screw conveyor 9. The mixtends to become compacted by the pressures in being struck off. As theexcess mix falls back into screw conveyor 9;, it is broken up andremixed, thereby being restored to a live condition. In this mannerthere is a continuous movement of excess bituminous mixture ahead of thescreed. The excess material is constantly being worked until it istamped under the sole plate and smoothed down into the furnished mat.There are no places in which excess mix accumulates and becomescompacted until a large lump breaks free.

Use of the invention enables bituminous paving to be laid atsubstantially higher speeds than has been possible heretofore withscreeds having tamper shields which extend only forwardly or which havesubstantial planar sections in them. A notable problem has been thelaying of mixes formed of fine aggregates, sometimes known as sheetasphalt, without tearing the finished mat. Since the customary practiceis to lay a base course of large aggregate and to reduce the size of theaggregate as each succesive course is laid, the problem of tearing ofthe final course makes the problem most pronounced where it cannot beobviated by a later course. The exact speed at which a course of sheetasphalt can be laid without tearing depends upon many things such as themix used, the weight of the screed, and its unit pressure. When thesefactors are alike, the maximum speed which can be reached withouttearing is quickly established by trial and error.

By way of comparison, a paver having a conventional screed heretoforetypifying good design was used on a particular asphaltic mix of fineaggregate. That paver reached a maximum speed of about twenty feet perminute without tearing the mat. When, however, a paver having a screedof like weight and size but embodying the invention was used on the samemix, paving speeds of up to seventy three feet per minute weresuccessfully maintained.

While I have illustrated and described a present preferred embodiment ofmy invention, it is to be understood that i do not limit myself thereto,and that my invention may be otherwise variously practiced within thescope of the following claim.

I claim:

Bituminous paving apparatus comprising a screed having sole plate meansfor smoothing bituminous material into a mat, a transversely extendingtamper positoned at the forward edge of the sole plate means andarranged for up and down axial reciprocating motion, said tamper havingits upper end rearwardly of its lower end, a tamper shield positionedforwardly of the tamper and initially sloping upwardly and rearwardlyfrom its lowermost portion at substantially the same angle to thevertical as the tamper, sloping upwardly and rearwardly to a mid-pointand thence upwardly and forwardly to the uppermost portion of the tampershield, and bituminous material agitating and distributing meanspositioned forwardly of the tamper sheld in position to agitate andredistribute bituminous mix struck oif by the screed.

References Cited by the Examiner UNITED STATES PATENTS Barber 94-46Barber 94-46 Mentes 94-46 Widelo 94--46 Schrimper 94-46 CHARLES E.OCONNELL, Primary Examiner. 10 N. C. BYERS, Assistant Examiner.

